1. Field of the Invention
The present invention relates to a plurality of tooling operations for forming pull tab easy open can ends. In particular, the present invention concerns the employment of a resilient tool support means mounted either between the press ram and an upper tool member, or between a lower tool member and the support bed. The resilient tool support means controls the penetration and clearance of the tooling in the closed position.
2. Prior Art
In the early days of easy opening can end production, it was recognized that the control of the movable ram mounted tooling in the true closed position was absolutely necessary in order to control remaining metal thickness, particularly in the scoring operation. Attempts were made to permit the scoring tool to project the correct distance so that the remaining metal, after the scoring operation, would be within the desired range of thicknesses. There were two problems with this technique, namely, metal gauge thicknesses were not as tightly controlled in the early days as compared to the present, and tight metal clamping. For example, if heavier gauge metal were employed in the scoring operation, a greater thickness of the remaining metal would result after the scoring operation, thus making the end of the easy open cans difficult to open. Conversely, thinner gauge thicknesses would be scored too deeply such that the cans would leak through the scored area, particularly when filled with carbonated beverages under pressure. Additionally, if the metal blank is clamped too tightly by the press, the metal will be unable to properly shift during scoring, resulting in small fractures in the remaining metal.
In order to avoid the problems of tight metal clamping and uncontrolled metal thicknesses, the invention set forth in U.S. Pat. No. 4,377,084 discloses scoring press apparatus having resilient stop blocks. In particular, this reference discloses typical press apparatus with a pair of resilient stop blocks mounted upon the stationary press floor. Atop each of the resilient stop blocks is a solid stop block which extends upwardly to the press ram. The resilient stop blocks progressively remove inherent clearances in the press in order to accurately determine the thickness of the remaining or residual metal which serves to firmly secure the scored element to the metallic sheet.
Because the arrangement of the stop blocks enabled the press to accurately determine the thickness of the residual metal, the press was capable of scoring different thicknesses of metallic sheet so that the residual metal remained a constant thickness. Although this device performed well, it was recognized that more precise control of the ram in the closed position was absolutely necessary for present needs employing thinner metallic sheets or blanks, to control the depth of penetration and the remaining metal thickness.
Presently, base metal gauge thicknesses have been more uniform such that a total variation from nominal thicknesses does not exceed .+-.0.0004 inches. This variation permits the use of new tooling techniques, including the use of a resilient tool support means, for a plurality of tooling operations, which is the subject of the present invention.